Method for making packaging particles and resulting product

ABSTRACT

The invention relates to sheet-like plastic packaging particles formed with a normally curved configuration having two spaced apart, curved, coextensive surfaces, one of said surfaces being a substantially unfoamed skin and the remainder of said particle including the other surface being foamed, and to methods for producing packaging particles which comprise warped or distorted, foamed sheet particles suitable for use as packaging particles from an extrudable, expandable synthetic plastic material, such as, a polymerized vinyl aromatic monomer, e.g., styrene, comprising the steps of extruding a foamed sheet of the material while chilling one surface thereof more rapidly than the other surface thereof as it is extruded to form on said one surface a skin of substantially unfoamed material or of higher density material than said other surface and the remaining portions of the sheet, thereafter, cutting said sheet to form sheet like pieces of the desired configuration and subjecting said pieces to heat at a foaming temperature to cause further foaming and distortion of said pieces to form a curved configuration.

This is a division of application Ser. No. 632,073, filed Nov. 14, 1975now U.S. Pat. No. 4,042,658.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to particulate packing material for use as dunnagefor providing protection to articles during shipment by absorbing shocksand by isolation of the articles from the walls of the shippingcontainers by means of the packaging particles. The invention is basedon the discovery that extruded foamed sheet of polymerizable vinylaromatic monomers, such as styrene, having a skin on only one surfacethereof can be caused to warp or distort to provide curvedconfigurations by the application of heat at temperatures at and abovethe foaming temperature. The present invention is also based on thediscovery that the direction of axial orientation of the sheet inrespect to the longest or shortest dimension (not thickness) of theparticle effects the shape and ultimate curved configuration of thewarped or distorted packaging particle after heating. Thus, small stripsof foamed thermoplastic sheet having a skin on one side only and havinga major dimension in the machine direction, e.g., in the direction ofextrusion, provides substantially different shapes and curvedconfigurations than particles made by heating strips cut from foamedsheets transversely to the machine direction. Furthermore, it wasdiscovered that packaging particles made by heating strips cut from suchfoamed sheets on a bias to the machine direction are significantlydifferent in shape from either of the above-mentioned particles and thatpackaging particles made by heating plastic sheet pieces having nolongest or shortest dimensions are also significantly different in shapethan any of those mentioned above.

The present invention permits the production of packaging particleswhich are free-flowing, which do not tend to interlock and which are ofexceedingly low bulk density.

The present invention is particularly adapted for use in thosecircumstances where the foamed sheet having a skin on only one sidethereof is produced at one location and sent to the location or areawhere the packaging particles will be made and used. In this manner,considerable shipping space and expense as well as storage space andexpense is conserved because the foamed sheet disposed in rolls does nottake up nearly as much space as the shaped, curved particles. At the uselocation or area, when the need arises for packaging particles, therolls can be cut into the desired flat shapes and then heated to thefoaming temperature or above to cause further distortion or warping andfoaming of the particles into the desired curved configuration. Thefoamed sheet can be cut into any desired patterns to produce various andsundry shapes and configurations. Additionally, adjustments to thebiaxial orientation and the relation of the major and minor dimensions(not thickness) to the direction of orientation can result in an evengreater variety of different forms and curved configurations.

The present invention is carried out by forming on a plastic sheet beingextruded a skin of higher density material than the remaining portionsof the sheet. The advantages and benefits of the invention are notobtained when no skin is formed on either surface of the sheet and arenot obtained when a skin of substantially the same density is formed onboth surfaces of the sheet. The advantages and benefits of the inventionresult only when the skin of high density material is formed on just onebut not both surfaces of the foamed extruded sheet.

2. Description of the Prior Art

There exists a worldwide market for a product generally referred to aspackaging particles or plastic dunnage. Other terms for the product are"loose fill" and the "free flow". The first product used in thisapplication was popcorn. Present day packaging particles are usuallymade of polystyrene foam. More specifically these particles are made ofa very small celled foam with an actual density of approximately 1 poundper cubic foot. They are reduced to this density from their extruded,expanded form by passing the extruded, expanded form through a steamexpander such as that which is used in the steam chest molding processof molding foamable polystyrene beads. The expander is a unit whichsubjects the particles to direct steam action which is very effective inreducing the density of polystyrene foams.

Many attempts have been made to provide packaging particles andparticles made from plastics, such as foamed polystyrene, have beenmarketed. U.S. Pat. Nos. 3,723,240, 3,400,037 and 3,251,728 and thepatents mentioned therein, illustrate the prior attempts to producepackaging particles some of which have been marketed and others of whichhave not. U.S. Pat. No. 3,723,240 describes several of these prior artattempts. This patent itself relates to the treatment of foamablestrands of polystyrene to impart asymmetry to the strand prior toexpansion by heating, that is, the strand is treated on one side thereofso that it expands on that side to a lesser degree. The treatment can bea scraping treatment, a heat-deforming treatment, the application of aplasticizer, and the positioning of a relatively non-foaming orrelatively low foaming element eccentrically in the strand. Duringsubsequent heat treatment, the elongate strand forms a foamed coilstrand having a helical configuration. This patent, however, fails todisclose or suggest the utilization of foamed but still foamable sheetsof thermoplastic resins, such as styrene and having only one surfacethereof formed with a skin, or more dense layer, to produce a widevariety of different configurations. Furthermore, the production rate ofthe method of this patent is comparatively low whereas the packagingparticles of the present invention can be produced at much greater ratesof production.

U.S. Pat. No. 3,400,073 teaches a method for making packaging particlesby extruding filaments, rods, or strands followed by slicing same andheating the sliced chips to expand same. The method of this patent islimited to low production rates as compared to production rates of themethod of the present invention. In addition, the resulting packagingparticles possess a relatively higher bulk density than some of theother prior art particles.

Other patents in the field of producing packaging particles include U.S.Pat. Nos. 3,026,273, 3,188,264, 3,281,895, 3,723,237. Additional patentsin this general area are U.S. Pat. Nos. Re. 27,243, 3,066,382,3,481,455, 3,829,269, 3,855,053, and 3,887,672.

Furthermore, the production of foamed sheets having a skin of unfoamedmaterial, or of a higher density material than the remainder of thesheet thickness, has been known for many years as illustrated by U.S.Pat. Nos. 3,311,681 and 3,560,600, the disclosures of which areincorporated herein by reference. These patents produce a foamed plasticsheet by extruding an expanded tube or bubble of polystyrene foam sheetand contact one surface of the tube with cooling gas or cooling surfaceto congeal that surface with little or no foaming while the remainder ofthe tube thickness and the other surface continues to foam. There is noteaching or suggestion in these patents to cut the resulting foam sheetinto sheet-like pieces and subject same to heat to post-expand them.

There has been much patent activity in the packaging particle field.Almost all of the patents have had to do with the shape of the particleinasmuch as the goal is to further reduce the bulk density of theparticles to at least as low as 0.5 pounds per cubic foot. Bulk densityis measured by placing the particles loosely in a cube container such asa 12 inches × 12 inches × 12 inches box. The weight of the particles forthis cubic foot volume is the bulk density and includes the air voidsaround the particles. Therefore, a particle with a shape that allows formuch void area would have substantial economic value since the productis measured and used on a volume basis rather than a weight basis. Hencea useable particle with the lowest bulk density is most desirable. Mostof the patents mentioned above relate to extruded strands of a constantcross section. These cross-sections are circular (Alta-Pak), a muted "S"(Pelapan Pak), a trilobular (Pakon, Tektronix) and a double tube or an 8shape (Foam-Pak). All of these are strands extruded continuously andpassed through a cutter station so that the constant cross sectionstrand is cut into one half inch or so lengths. There are variations tothis cutting length since some products are produced so that in theunfoamed state they may be 1/8 to 1/4inch in length. Other products aresliced and curl during the post-expansion. It is these cut-off sectionsof foam particles that are post-expanded as mentioned earlier.

One of the more serious problems with the just mentioned prior artparticles is production rate. Since the expansion is great, the actualorifices from which they are extruded are quite small. A single orificewill produce about ten pounds per hour. A small extruder runs with sevensuch strands for a total production rate of 70 pounds per hour. This istypical of the size extruder and rates used in producing the prior artparticles. A foam line with a production rate of 300-600 pounds per hourwould be almost unmanageable in terms of the number of strands neededfor this increased production rate.

By the process of this invention, particles can be produced as fast asany foam line is able to run. In other words, if a 41/2-6 inches dualextruder foam line is capable of producing 600-700 pounds per hour offoam, then it could produce 600-700 pounds per hour of packagingparticles.

One of the other objections to the packaging particle business is theshipping and storage of the prior art particles. A 15 cu ft bag holdsonly 71/2 pounds of post-expanded particles. Therefore, shipping andstorage of the prior art particles can be an immence undertaking. Theprocess of this invention has the ability to overcome this problem too.

SUMMARY OF THE INVENTION

A conventional polystyrene foam sheet extrusion line is the basicmachinery which can be used in the process of this invention. Suchextrusion lines usually use dual or tandem extrusion lines such as a41/2 inch extruder feeding a 6 inch extruder; 31/2 inch feeding a 41/2inch extruder and both larger and smaller versions of this tandemconcept. Lengthened single screw extruders and twin screw extruders canproduce such foam sheet as is required for the process of thisinvention. A foam sheet extrusion line usually comprises the basicextruder with its associated feeding and gas injection system; a tubularextrusion die, a holding-while-cooling device which can be a sizingmandrel or a trapped air bubble system, draw rolls and sheet winders. Animportant addition that is needed for the process of this invention iswhat is usually referred to as "skinning" step or device. That is, bysubjecting the foamable extrudate immediately as it leaves the extruderdie to a curtain of cold air or contacting the extrudate immediatelywith a cold surface such as a chilled ring, the surface of the expandingfoam can be quickly quenched so that the gas at this surface layer doesnot expand the polystyrene or expands it to a much lesser extent thanthe remainder of the extrudate.

This technique has been used heretofore (U.S. Pat. No. 3,311,681) forthe purpose of producing a relatively hard surface on the foam so it canbe used in making dishes which resist cutting and puncturing by knivesand forks. It is also used in the foam egg carton field to produce asmooth surface which accepts printing quite well. Inasmuch as thetubular foam sheet is biaxially stretched as it leaves the die, theunfoamed skin becomes a highly biaxially oriented film, and still is anintegral part of the foam sheet structure. As it moves away from thedie, the uncooled and expanding cellular foam beneath this skin is notnearly as biaxially oriented since it must be taken off biaxiallysufficiently quickly so as to minimize the tendency of the foam towrinkle or corrugate. This happens when the foam is expanding threedimensionally at a faster rate than it is being stretched during thetake away portion of the operation. Consequently, the skinned foam sheetis a composite of a highly oriented, potentially biaxially orientedsubstantially non-foamed film skin and a low density, low biaxiallyoriented cellular foam structure.

I have discovered that if this foamed and skinned sheet is cut intosmall pieces such as one inch by one inch and subjected to apost-expansion technique, such as by contacting with steam, boilingwater or radiant oven heat, the pieces will expand in the foam portionsof the piece while the skinned or substantially unfoamed surface willcontract depending upon the kind and relative direction of orientationit was subjected to. This creates a curled or bent particle having anactual density as low as one pound per cubic foot and sufficientcurvature of the particle to provide air voids creating an overall bulkdensity of one half pound per cubic foot. The key to the process is insubjecting particles cut from "skinned" foam sheet to a post-expansionheat treatment which expands the foam to a low density while causingsufficient shrinkage of the skin portion resulting in curling of theparticle to further reduce the bulk density.

The following production equipment can be used in this invention. Asstated earlier the foam can be extruded on a standard polystyrene foamsheet line and can be subjected to the skinning effect on one side only,usually the outside, as it is extruded from the die. The sheet can bewound in the usual manner. However, for practical applications, it maybe preferable to slit the foam sheet into narrower widths such as 6 to12 inches, more or less, although this should not be considered alimitation. These widths could be easily fed into available pelletizerswhich are usually manufactured to cut pellets into one eighth inchpieces. However, by modification as to the number of blades and theratio of draw roll speed to cutter knives rotation, the length of cutcan be changed considerably. Lengths of one quarter inch to one inchwould be quite simple to produce. If such a pelletizer were furtherequipped with slitting knives just before the pelletizing cutter blades,the foam sheet could quickly and economically be cut into the desiredshapes. Such shapes could be squares such as one inch by one inch orthree quarter by three quarter inch. Also rectangular pieces such as onequarter by one inch or one and a half inches could also be made withthis set-up. Also, cutting rolls can be used to cut a wide variety ofdifferent shapes which ultimately produce particles of very interestingconfigurations. Sheets which I cut at 45° to the direction of extrusion,for example, post-expanded into corkscrew shapes.

The control and adjustment of orientation in the foam sheet and theshape of the pieces cut from the sheet can create a wide variety ofshapes upon post-expansion. Also, the slitters can be set up to cut avariety of widths instead of only one size. This might be advantageousin creating the lowest possible bulk density. Orientation in the skinnedfoam sheet can be varied to obtain optimum low bulk density. Adjustmentsto the blow-up ratio and draw-down or take off speed of the tube orbubble extruded can be used to induce equal or unequal biaxialorientation. For example, a low blow-up ratio and a high lineal or drawdown rate could produce foam that is highly oriented in the machinedirection (i.e. direction of extrusion). This can be further affected bythe degree of skinning given to the foam. If a small amount of coolingair is blown onto the foam, only a thin skin will be created and itsability to contract or cause curvation would be relatively small. If alot of cooling air or colder air is blown, a heavy skin can be createdand it can be highly oriented depending upon how much it is beingstretched. Too much skin can create too high a density. It is desirablethat there be sufficient skinning to create a curvature shaping actionduring post-expansion without being detrimental to the overall density.Further versatility can be realized by using rotary cutters havingcutter blades of other shapes than straight. For example, chevron or "V"shaped parts can be made with a large serrated blade; also "C" shapes,"W" shapes, half or quarter moon shapes. Placing the many possibleshapes in conjunction with varying the orientation and cutting theshapes on a bias from the directions of orientation can producetremendously versatile packaging particles. The variety of shapes thatcan be cut from this sheet is unlimited and the choice of these shapesgive versatility to the process in terms of dynamic cushioning, bulkdensity and flow characteristics. It also has considerable marketingpotential inasmuch as shapes of the alphabet, numbers, initials, starsand even a variety of shapes cut from the same sheet permits thepackaging particles to be produced in ornamental or decorative shapesand configurations.

There is another advantage to the process described herein. It is veryexpensive to ship the big bags of packaging particles. The rolls ofskinned foam could be shipped, either slit to width or as master rollsto distant plants which would have the modified cutters and the steamexpanders. Consequently, only the rolls would be stored and when acustomer orders packaging particles, they would be made by running therolls of skin foam through the cutter and expander, put in the largeshipping bags and shipped immediately to the customer, therebyminimizing storage space required for this product. The foam rolls couldhave a bulk density of 2 to 10 pounds per cubic foot as compared to the0.5 pound per cubic foot of the finished product. Shipping costs wouldbe reduced by the same magnitude.

It is noted that there is a difference in the skinning effect whendifferent blowing agents are used. Freon 12 or Genetron 12 allows theformation of an easily produced skin that renucleates to a microscopiccell size on the skin when it is reheated. Foams made with pentane donot have the renucleation effect as pentane appears to leave the skinsurface leaving a substantially unfoamed biaxially oriented film.Pentane or any other suitable blowing agent can be used.

Also, the basic thickness of the foam sheet will have quite an effectupon the cushioning and density characteristics of the resultantpackaging particles. Again, this is a part of the versatility of thisprocess as it can be easily modified to fit the cushioning propertiesrequired.

It is also possible that a roller cutter could be used that would giveunlimited shapes cut from the sheet. Narrow tapes or non-tubular sheetsas are described by Winstead, U.S. Pat. No. 3,789,095 can be used as thesheet in this process inasmuch as a skin can be placed on these foamsheets.

The skinned foam sheets utilized herein can be made on a tube die ortape die. The tube die gives us the capability of creating both a linealand cross orientation, i.e., orientation in the machine direction aswell as the direction transverse thereto. Die openings, choice ofdirections and degrees of orientation, density and cell size can becontrolled to create packaging particles of a wide range of uniqueproperties. As stated earlier, the variety of shapes is unlimited.

I have mentioned mostly air as the means used for skinning the foam asit is the most commonly used process. However, skins can be produced onfoams by contacting the foam with water or water cooled or chilled metalrings or devices. An interesting concept is to place cooled metaldevices both inside and outside of the tubular extrudate in such amanner that the foam was alternately skinned on the two surfaces. Inother words, where it had a skin on the outside, there would be no skinon the inside and vice versa. When such a sheet is then oriented and cutinto packaging particles, the alternating skins would cause contractionsand expansions such that the sheet could have a cross section similar toa sine wave. Rectangular particles could take the post-expanded shape ofan "S" with the skin being on the inside of the two curvatures. Cuttingthis sheet on a bias into the various designs, the possible number ofdifferent post-expanded shapes is unlimited. It is also possible thatthe sheet be made not completely flat. By placing grooves or notches onone die lip or both die lips, a varying thickness of foam or even acorrugate sheet could be made and skinned as described herein. Such agrooved sheet might take up more space and create a lower bulk density.Alternating thick and thin spots can create more air voids and also dounusual things in the distortion caused by the post-expansion. Holes canbe cut in the sheet so that a grid was being run through the slittercutter. Both the parts cut from the grid and the parts cut as the holescould be expanded and used as packaging particles.

The above description refers to polystyrene foam since it does axiallyorient upon stretching, post-expand with steam and bend with thecontraction-expansion phenomenon which imparts curvature to the finishedparticles. Polyethylene foam does not. However, it can be slit and cutinto pieces that can be added to the polystyrene foam particles so as toenhance the packaging characteristics of the overall product.

The foamable thermoplastic resin compositions which can be extruded bythe method and apparatus of this invention consists of a thermoplasticresin and a suitable foaming or pore-forming agent. Examples ofthermoplastic resins that may be employed include those that can bechilled on the surface to produce a skin which is capable of beingaxially oriented such that upon post-expansion there results thecontraction-expansion phenomenon which imparts curvature to the finishedparticles.

In general, optimum results are obtained with rigid, relativelynon-elastic thermoplastic resins such as homopolymers and interpolymersof vinyl chloride, homopolymers of vinyl aromatic hydrocarbon compoundsand ring halogenated derivatives thereof, e.g., styrene,o-chlorostyrene, p-chlorostyrene, 2,5-dichlorostyrene,2,4-dichlorostyrene, p-methylstyrene, p-ethylstyrene, vinyl naphthalene,alpha-methylstyrene, and interpolymers of such vinyl aromatic monomerswith other vinyl monomers, e.g., acrylonitrile, or other vinyl monomerscopolymerizable with styrene, in which the interpolymer contains atleast 70% of the vinyl aromatic hydrocarbon compounds. It is feasibleand sometimes desirable to employ a blend of two or more thermoplasticresins such as a blend of styrene and a rubbery polymer, e.g., naturalrubber, butadiene-acrylonitrile rubbers and the like. High impactpolystyrene prepared by polymerizing monomeric styrene in the presenceof a rubbery diene polymer also may be employed advantageously.Moreover, scrap plastic material, e.g., polystyrene comprising trimmingsand rejects from other plastic forming operations can be used as well asgeneral purpose or virgin plastics.

Suitable foaming agents for the thermoplastic resins are well known andthe selection of the particular foaming agents to be employed will bedictated largely by the particular thermoplastic resin in which it is tobe incorporated. It is preferred to employ as foaming agentsnon-reactive organic liquids which have not more than a slight solventaction on the thermoplastic resin and which volatilize below thesoftening point of the thermoplastic resin. Such agents include theseboiling between 80° F to 200° F. Examples of suitable foaming agentsthat may be employed include pentane, hexane, heptane, petroleum ether,cyclopentane, cyclopentadiene, acetone, methanol, methyl acetate, ethylacetate, methyl formate, ethyl formate, dichloroethylene, isopropylchloride, propionaldehyde, diisopropyl ether, the fluorinatedhydrocarbons including the Freons, e.g., Freon 11 (CCl₃ F) or Freon 12(CCl₂ F₂), the Genetrons and the like. Mixtures of blowing or foamingagent can be used, e.g., mixture of a fluorocarbon and pentane. Usuallythe foaming agent will be employed in the amount of about 21/2 - 10 andpreferably 5-8 weight percent of the thermoplastic resin.

The thickness of the skinned, extruded, foamed sheet beforepost-expansion can range from 40 or 50 to 250 thousandths of an inch,preferably 60 to 125 thousandths of an inch and most preferably 90 to100 thousandths of an inch. The post-expanded product has a thickness of80 to 100 to 500 thousandths of an inch, preferably 150 to 250thousandths of an inch. The thickness of the skin itself varies fromabout 0.25, preferably about 0.5, thousandths of an inch thick on thethinnest post-expanded products to about 5.0, preferably about 3.0,thousandths of an inch thick on the thickest post-expanded products.

There is another unique characteristic of the packaging particles ofthis invention. All of the prior art particles are substantially equaldensity throughout. With the skin affect used in this invention there isproduced a foam particle which has a soft and resilient material on theouter surface but has on the inner surface a thin layer of almost solidhigher density, relatively stronger material which is integrally bondedto the lower density foam. Such a composite structure can be stated tohave a more rigid, stronger character and consequently is a superiorform of packaging particles. The higher density, relatively stronger"skin" material reinforces the particle to render it more resistant tocrushing without sacrifice in bulk density or presentment of a soft sideto the article being packaged.

The skinning affect on polystyrene foam is not dependent upon the actualthickness of the overall sheet. Therefore, a skin can be placed on afoam sheet from a minimum of perhaps 0.40 inch or less thickness and ona foam as thick as 0.250 inch or more. This versatility means that withthe very same equipment, there can be produced flowable, loose fillcushioning particles of varying bulk density, dynamic cushioningproperties, and settling characteristics. The very thin foamed particlesof this invention could be used for extremely fragile articles such asmissile guidance systems and precision aligned test instruments whichrequire fragility factors of 15 to 25 G's. With increases in thickness,the novel packaging particles can handle rugged machinery with fragilityfactors above 100 G's. This could be done with the very same density ofproduct. The prior art packaging particles would either have to increasethe density and therefore the cost of the product or change to anentirely different shape to create the versatility of handling the fullrange of extremely fragile to rugged articles. Most packaging particlesappear to be less than 1.5 inches in maximum dimension to be freeflowing. To get maximum advantage of curvature, particles of 1 to 11/2inches appear to be most desirable. Particles that are too small may nothave sufficient curvature or proper shape to create the large air spacesthat are needed to create the low bulk density. In the presentinvention, packaging particles range from about 0.5 inch to about 3.0inches or higher, preferably about 1.0 to about 1.75 inch in theirmaximum dimension.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic view partially in section and partially cutaway of an embodiment of this invention for producing a skinned foamedsheet and slitting it into strips of smaller width;

FIG. 2 is a diagrammatic view in perspective illustrating an embodimentof this invention wherein the strips of narrower width produced in themanner shown in FIG. 1 are further slit and cut into particles which arefed to a post-expander where they are post-expanded and thence fed bypneumatic means to storage or packaging; and

FIG. 3 is a perspective view of one type of particle produced by thepresent invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown the delivery end of a conventionalscrew-type extruder 10 having a circular die orifice 11 and a conicalinsert 12 around which the melt within the extruder flows beforeextruding through the die orifice 11 to form a tube of foaming plasticsheet 15. The conical insert 12 also supports a cylindrical sizingmandrel 13 by means of a supporting bar or rod 14 extending in front ofthe die orifice 11. The screw-type extruder may be of the same type asdisclosed in U.S. Pat. No. 3,311,681 which also describes a typicalsizing mandrel 13 and supporting rod 14. However, instead of directingcooling air on the inner surface of the extruded, foaming sheet 15 asshown in U.S. Pat. No. 3,311,681, a cooling air ring 16 is providedaround the orifice 11 to impinge cooling air on the foaming sheet 15 asit emerges through orifice 11. The cooling air ring 16 is provided witha circular opening 17 along its inner periphery for directing coolingair onto the tube of extruded foaming plastic sheet 15 as it emits fromthe die orifice 11. The cooling air chills the outer surface of theexpanding tube to congeal it and form a skin thereon. The inner surface,however, is allowed to expand to its normal extent and the tube is sizedand shaped by the mandrel 13 in the conventional way. The lower side ofthe tube is slit by slitter 18 and the tube 15 is drawn by draw rolls19, 20, at the desired rate of speed consistent with the degree ofbiaxial orientation desired. The draw rolls also serve to flatten theslit tube which is further slit by slitters 21 to form a plurality ofrolls of foamed sheet having an unfoamed skin on one surface thereof.These sheets are wound into rolls 22 which then may be stored or shippedto the location of use or immediately used to produce the packagingparticles of the present invention.

Referring to FIG. 2, a roll 22 of skinned, foamed sheet is unrolled andpassed through feed rolls 23, through a slitting device 24 which slitsthe sheet into strips and thence to a rotary cutter 25 which chops thestrips into pieces 26. The pieces 26 are fed into a funnel-shaped infeed27 to a pipe 28 of a pneumatic conveyor 29 which delivers the piecesthrough pipe 30 into post-expander 31 where it is heated, for example,by the live steam, to post-expand the pieces 26 to form the packagingparticles 38 of this invention. The thus formed packaging particles 38exit from the expander 31 through exit tube 32 which delivers them intoa funnel-shaped infeed 33 to pipe 34 of pneumatic conveyor 36 whichsends the particles 38 through pipe 37 to storage or to a packagingdepartment where the particles 38 are used for packaging other productsor where they themselves are packaged in bulk for shipment to a customeror another site of use.

The packaging particle 38 is shown in perspective in FIG. 3 and includesa skinned concave surface 39. The remainder of the particle 38 comprisesa foamed portion 40. The pieces 26 can be cut into any desiredconfiguration such as chevrons, circles, rectangles, squares, triangles,W's, L's, T's, V's, Z's arcuate, zig-zags, four-pointed stars,five-pointed stars, octagons, hexagons, pentagons, any combinationsthereof, or any other configuration desired. The curling due todifferences in shrinkage and expansion capabilities of the skinned andfoamed portions of the pieces 26 during post-expansion provides thepotential for producing packaging particles 38 of a very wide variety ofdifferent shapes and forms.

EXAMPLE 1

A dual extruder foam extrusion line consisting of a 41/2 inch extruderfeeding a 6 inch cooling extruder was operating at 600 pounds per hour.Virgin polystyrene was used as a raw material and 6% of Freon 12 (basedon the weight of the polystyrene) was injected into the system. Thecooling extruder was equipped with a circular die having an openingwhich was 7 inches in diameter and 0.010 inch thick. There also wasutilized a 28 inch diameter sizing mandrel situated in front of the dieand spaced therefrom. The extrusion line formed a cylindrically shapedextrusion which passed over the mandrel. The tubular foam extrusion hada diameter of about 28 inches and was slit to produce two sheets of 42inches width × 0.100 inch thick. The actual density of the sheets was5.6 pounds per cubic foot. Fitted around the 7 inch diameter circulardie was an air ring that blew cold air on and chilled the outer surfaceof the foam sheet immediately as it left the die. The air that passedthrough the air ring was prechilled to 45° F by passing it through arefrigerating unit. The cold air caused a solid skin to form on the foamsheet integral therewith and which measured 1.5 mils or thousandths ofan inch thick. The sheets were directed to a dual winder where they werewound and at the same time slit into 14 individual rolls of 6 inch widesheet. The rolls were stored for 24 hours.

The sheet from one 6 inch roll was then passed through a slitter-cuttingdevice that cut the sheet into chevron shaped packaging particles, 11/2inches wide overall, 1 inch in overall length with an actual width ofthe arms of the chevron, that was 3/8 inch. From the slitter-cutter, thechevron shapes were pneumatically blown to a steam expander. Whensubjected to live steam heat in the expander, the chevron particlesexpanded to a thickness of 310 mils or thousandths of an inch. Thedifferential expansion and contraction caused by the foam part expandingand the skin side shrinking caused a warpage of the chevron so that ittook a spherical shape, i.e., as if it had been cut from a sphere havinga diameter of 1.25 inches. The actual density of the expanded productswas 1.09 pounds per cubic foot and the bulk density of these packagingparticles was 0.6 pounds per cubic foot. The packaging particles werefree flowing, passing freely through a storage container having a 5 inchdiameter loading nozzle.

EXAMPLE 2 (COMPARISON)

This is not an example of the present invention but compares packagingparticles made from foamed plastic sheet on which no skin was formedwith the packaging particles of Example 1. The same operation asdescribed in Example 1 was carried out with the exception that the airring was not used. The foam sheet was 0.110 inch thick and had an actualdensity of 5.0 pounds per cubic foot. Since the air ring was not used,no skin was created on the foam and it was of uniform density and cellstructure throughout. Twenty-four hours later when this sheet was passedthrough a slitting-cutting device, made into the chevron shapes, andpassed through the steam expander, all in the same manner as describedin Example 1, the chevrons expanded to an actual density of 1.0 poundper cubic foot. However, no distortion was created in these particlesand they expanded to basically flat chevrons having a thickness of 325mils thousandths of an inch 1.7 inches wide overall and 1.25 inches inoverall length. The bulk density of packaging particles was 0.8 poundper cubic foot. They did not flow freely through the storage vessel dueto excessive interlocking of the particles.

EXAMPLE 3

A 31/2 inch diameter screw extruder that had been extended to an L/Dratio of 44 to 1 was utilized to produce polystyrene foam sheet. The rawmaterial used was pelletized polystyrene made from 100% scrap materialfrom the production of foamed polystyrene meat trays and egg cartons,and crystal polystyrene cocktail tumblers and the purgings created fromthe initial start-up of foam extrusion equipment. The blowing agentcomprised of a mixture of 50% Freon 12 and 50% Freon 11. Thiscombination blowing agent was injected into the extruder at a rate of11.4% based on the weight of polystyrene, creating a foam with an actualdensity of 2.8 pounds per cubic foot. A 5 inch diameter circular diewith a 0.007 inch wide die opening was utilized with a 15.6 inchdiameter sizing mandrel to produce a tube of about the same diameterwhich was slit to provide a single sheet about 48 inches wide. An airring was placed around the die so that cooling air was impinged on theouter surface of the foam extrudate immediately as it left the die. Thesame outer surface of the sheet was then immediately made to contact awater cooled hollow cylindrical cooling plate having an internaldiameter of 7 inches. The combination of the air cooling and contactwith the water cooled metal plate resulted in a foam sheet of 0.075 inchthickness having a skin 0.0025 inch thick integral with the foam sheet.The sheet was directed to a winder where it was slit to 8 inch widthsand 6 such rolls were wound. The foam sheet rolls were stored for 48hours.

A roll of the foam sheet was then passed through a rotary die cuttersystem which cut the foam sheet into a variety of shapes, including theshapes of the letters L, J and W as well as squares, diamonds andtriangular shapes. From the rotary die cutter, the particles weredirected to a steam expander wherein the particles expanded anddistorted. The particles expanded to an actual density of 0.8 pounds percubic foot and a bulk density of 0.35 pounds per cubic foot. All of theparticular shapes warped extensively in proportion to the primary linealorientation which was induced into the foam sheet. The packagingparticles of the various shapes were free flowing and were used topackage light-weight delicate instruments.

EXAMPLE 4

Using the same 8 inch wide rolls produced in Example 3, straight piecesof foam sheet were cut parallel to the axis of extrusion and,respectively, 45° and 30° from the axis of extrusion. Those pieces cutparallel to the axis of extrusion were 3/8 inch wide, cut in lengths of11/2 inches, 2 inches and 3 inches. When placed in boiling water, the11/2 inch pieces distorted to become a portion of a hollow cylinderhaving a semi-circular cross section, a diameter of 1.25 inches and awidth of one half inch. The 2 inch pieces distorted to a hollowcylindrical C-shape having a 1.25 inch diameter with about 270° of thecircular cross-sectional shape. The 3 inch piece distorted in boilingwater to become a perfect hollow cylinder with the ends actuallytouching and having a diameter of 1.25 inches. All three shapes weresuitable as packaging particles although the semi-circular and C-shapedparticles did interlock and therefore did not flow quite so freely.

The pieces cut at a 45° angle were cut 33/4 inches in length by 3/8 inchwide. When subjected to boiling water, these pieces distorted to acorkscrew shape having a pitch of 1 inch and a clearance of 1/2 inchbetween the threads. Pitch diameter was 13/8 inches. The pieces cut at30° from the axis of extrusion were cut 6 inches in length. These alsoformed a threaded or corkscrew shape with no clearance between threads.The pitch was 1/2 inch and its diameter was also 13/8 inches. The solidskin portion of these pieces took a double concave structure impartingexcellent stiffness to the previously described shapes. Since the outerportion of the foam was constructed of a very resilient type foam, apackaging particle of superior quality was created having a strong,stiff solid inner layer covered by a soft resilient foam which is idealfor packaging purposes.

EXAMPLE 5

A twin screw extruder with an L/D ratio of 131/2 to 1 and 90 mil.diameter screws was used to produce polystyrene foam sheet, at a rate of50 pounds per hour. 100% Freon 11 was used as a blowing agent at a rateof 12.1% based on the weight of polystyrene creating a foam sheet havinga density of 3.7 pounds per cubic foot. A flat tape die 2 inches inwidth by 0.025 inch thick was positioned in a downward direction so thatone surface of foam extruded from it was immediately contacted withwater having a temperature of 70° F. The foam sheet was drawn andoriented extensively in the lineal (machine) direction. The resultingfoam sheet was 5 inches wide, 0.125 inch thick and had an integral skin0.004 inch thick on one surface. The sheet was stored for 48 hours, thenfed through a roller die cutter having the random die cutting shape of ajigsaw puzzle to produce randomly cut pieces. When these randomly cutparticles were subjected to the steam expander, they distorted with alineal distortion proportional to the orientation induced into the foamsheet. The particles post-expanded to an actual density of 0.9 poundsper cubic foot and a bulk density of 0.45 pounds per cubic foot. Theparticles were free flowing and were used to package delicate electronicparts.

What is claimed is:
 1. A sheet-like packaging particle comprised of apolymerized vinyl aromatic monomer formed with a normally curvedconfiguration having two spaced apart, curved, substantially coextensivesurfaces, one of said surfaces being concave and comprising asubstantially unfoamed skin and the remainder of said particle includingthe other said surface being foamed.
 2. Particle as claimed in claim 1wherein said vinyl aromatic monomer is styrene.
 3. Particle as claimedin claim 2 wherein said sheet-like particle has a coil configuration. 4.Particle as claimed in claim 2 wherein said sheet-like particle has acylindrical configuration.
 5. Particle as claimed in claim 2 whereinsaid sheet-like particle has a sphere-like configuration.